1======
2Kbuild
3======
4
5
6Output files
7============
8
9modules.order
10-------------
11This file records the order in which modules appear in Makefiles. This
12is used by modprobe to deterministically resolve aliases that match
13multiple modules.
14
15modules.builtin
16---------------
17This file lists all modules that are built into the kernel. This is used
18by modprobe to not fail when trying to load something builtin.
19
20modules.builtin.modinfo
21-----------------------
22This file contains modinfo from all modules that are built into the kernel.
23Unlike modinfo of a separate module, all fields are prefixed with module name.
24
25
26Environment variables
27=====================
28
29KCPPFLAGS
30---------
31Additional options to pass when preprocessing. The preprocessing options
32will be used in all cases where kbuild does preprocessing including
33building C files and assembler files.
34
35KAFLAGS
36-------
37Additional options to the assembler (for built-in and modules).
38
39AFLAGS_MODULE
40-------------
41Additional assembler options for modules.
42
43AFLAGS_KERNEL
44-------------
45Additional assembler options for built-in.
46
47KCFLAGS
48-------
49Additional options to the C compiler (for built-in and modules).
50
51CFLAGS_KERNEL
52-------------
53Additional options for $(CC) when used to compile
54code that is compiled as built-in.
55
56CFLAGS_MODULE
57-------------
58Additional module specific options to use for $(CC).
59
60LDFLAGS_MODULE
61--------------
62Additional options used for $(LD) when linking modules.
63
64HOSTCFLAGS
65----------
66Additional flags to be passed to $(HOSTCC) when building host programs.
67
68HOSTCXXFLAGS
69------------
70Additional flags to be passed to $(HOSTCXX) when building host programs.
71
72HOSTLDFLAGS
73-----------
74Additional flags to be passed when linking host programs.
75
76HOSTLDLIBS
77----------
78Additional libraries to link against when building host programs.
79
80KBUILD_KCONFIG
81--------------
82Set the top-level Kconfig file to the value of this environment
83variable.  The default name is "Kconfig".
84
85KBUILD_VERBOSE
86--------------
87Set the kbuild verbosity. Can be assigned same values as "V=...".
88
89See make help for the full list.
90
91Setting "V=..." takes precedence over KBUILD_VERBOSE.
92
93KBUILD_EXTMOD
94-------------
95Set the directory to look for the kernel source when building external
96modules.
97
98Setting "M=..." takes precedence over KBUILD_EXTMOD.
99
100KBUILD_OUTPUT
101-------------
102Specify the output directory when building the kernel.
103
104The output directory can also be specified using "O=...".
105
106Setting "O=..." takes precedence over KBUILD_OUTPUT.
107
108KBUILD_DEBARCH
109--------------
110For the deb-pkg target, allows overriding the normal heuristics deployed by
111deb-pkg. Normally deb-pkg attempts to guess the right architecture based on
112the UTS_MACHINE variable, and on some architectures also the kernel config.
113The value of KBUILD_DEBARCH is assumed (not checked) to be a valid Debian
114architecture.
115
116ARCH
117----
118Set ARCH to the architecture to be built.
119
120In most cases the name of the architecture is the same as the
121directory name found in the arch/ directory.
122
123But some architectures such as x86 and sparc have aliases.
124
125- x86: i386 for 32 bit, x86_64 for 64 bit
126- sh: sh for 32 bit, sh64 for 64 bit
127- sparc: sparc32 for 32 bit, sparc64 for 64 bit
128
129CROSS_COMPILE
130-------------
131Specify an optional fixed part of the binutils filename.
132CROSS_COMPILE can be a part of the filename or the full path.
133
134CROSS_COMPILE is also used for ccache in some setups.
135
136CF
137--
138Additional options for sparse.
139
140CF is often used on the command-line like this::
141
142    make CF=-Wbitwise C=2
143
144INSTALL_PATH
145------------
146INSTALL_PATH specifies where to place the updated kernel and system map
147images. Default is /boot, but you can set it to other values.
148
149INSTALLKERNEL
150-------------
151Install script called when using "make install".
152The default name is "installkernel".
153
154The script will be called with the following arguments:
155
156   - $1 - kernel version
157   - $2 - kernel image file
158   - $3 - kernel map file
159   - $4 - default install path (use root directory if blank)
160
161The implementation of "make install" is architecture specific
162and it may differ from the above.
163
164INSTALLKERNEL is provided to enable the possibility to
165specify a custom installer when cross compiling a kernel.
166
167MODLIB
168------
169Specify where to install modules.
170The default value is::
171
172     $(INSTALL_MOD_PATH)/lib/modules/$(KERNELRELEASE)
173
174The value can be overridden in which case the default value is ignored.
175
176INSTALL_MOD_PATH
177----------------
178INSTALL_MOD_PATH specifies a prefix to MODLIB for module directory
179relocations required by build roots.  This is not defined in the
180makefile but the argument can be passed to make if needed.
181
182INSTALL_MOD_STRIP
183-----------------
184INSTALL_MOD_STRIP, if defined, will cause modules to be
185stripped after they are installed.  If INSTALL_MOD_STRIP is '1', then
186the default option --strip-debug will be used.  Otherwise,
187INSTALL_MOD_STRIP value will be used as the options to the strip command.
188
189INSTALL_HDR_PATH
190----------------
191INSTALL_HDR_PATH specifies where to install user space headers when
192executing "make headers_*".
193
194The default value is::
195
196    $(objtree)/usr
197
198$(objtree) is the directory where output files are saved.
199The output directory is often set using "O=..." on the commandline.
200
201The value can be overridden in which case the default value is ignored.
202
203KBUILD_ABS_SRCTREE
204--------------------------------------------------
205Kbuild uses a relative path to point to the tree when possible. For instance,
206when building in the source tree, the source tree path is '.'
207
208Setting this flag requests Kbuild to use absolute path to the source tree.
209There are some useful cases to do so, like when generating tag files with
210absolute path entries etc.
211
212KBUILD_SIGN_PIN
213---------------
214This variable allows a passphrase or PIN to be passed to the sign-file
215utility when signing kernel modules, if the private key requires such.
216
217KBUILD_MODPOST_WARN
218-------------------
219KBUILD_MODPOST_WARN can be set to avoid errors in case of undefined
220symbols in the final module linking stage. It changes such errors
221into warnings.
222
223KBUILD_MODPOST_NOFINAL
224----------------------
225KBUILD_MODPOST_NOFINAL can be set to skip the final link of modules.
226This is solely useful to speed up test compiles.
227
228KBUILD_EXTRA_SYMBOLS
229--------------------
230For modules that use symbols from other modules.
231See more details in modules.txt.
232
233ALLSOURCE_ARCHS
234---------------
235For tags/TAGS/cscope targets, you can specify more than one arch
236to be included in the databases, separated by blank space. E.g.::
237
238    $ make ALLSOURCE_ARCHS="x86 mips arm" tags
239
240To get all available archs you can also specify all. E.g.::
241
242    $ make ALLSOURCE_ARCHS=all tags
243
244KBUILD_ENABLE_EXTRA_GCC_CHECKS
245------------------------------
246If enabled over the make command line with "W=1", it turns on additional
247gcc -W... options for more extensive build-time checking.
248
249KBUILD_BUILD_TIMESTAMP
250----------------------
251Setting this to a date string overrides the timestamp used in the
252UTS_VERSION definition (uname -v in the running kernel). The value has to
253be a string that can be passed to date -d. The default value
254is the output of the date command at one point during build.
255
256KBUILD_BUILD_USER, KBUILD_BUILD_HOST
257------------------------------------
258These two variables allow to override the user@host string displayed during
259boot and in /proc/version. The default value is the output of the commands
260whoami and host, respectively.
261
262KBUILD_LDS
263----------
264The linker script with full path. Assigned by the top-level Makefile.
265
266KBUILD_VMLINUX_OBJS
267-------------------
268All object files for vmlinux. They are linked to vmlinux in the same
269order as listed in KBUILD_VMLINUX_OBJS.
270
271KBUILD_VMLINUX_LIBS
272-------------------
273All .a "lib" files for vmlinux. KBUILD_VMLINUX_OBJS and KBUILD_VMLINUX_LIBS
274together specify all the object files used to link vmlinux.
275